(a) Technical Field
The present invention relates to a low pressure casting device. More particularly, the present invention relates to a cooling system for a low pressure casting device that cools molds when a cylinder head is cast at a low pressure.
(b) Related Art
A low pressure casting device injects, by feeding pressure of compressed air or inert gas, a molten metal into molds to manufacture casting products such as a cylinder head.
Such a low pressure casting device includes an upper mold, a lower mold, and side molds. A core pin of a spark plug is mounted at the upper mold, and an injection hole for injecting the molten metal and a mold portion of a combustion chamber corresponding to the combustion chamber of a cylinder head are formed at the lower mold.
The low pressure casting device injects the molten metal into an insert space of a core through the injection hole in a state that such molds are set around the core.
In addition, the molten metal injected into the insert space of the core undergoes cold forming and is formed into castings such as a cylinder head.
Meanwhile, cooling efficiency of the molten metal is a key factor in improving productivity of the castings.
According to conventional art, the molten metal is cooled by supplying cold air to a region close to the core pin of the spark plug of the upper mold and the injection hole of the lower mold.
However, since the region close to the core pin of the spark plug and the injection hole is locally cooled, the mold portion of the combustion chamber is not  uniformly cooled according to the conventional arts. Accordingly, dendrite arm spacing (DAS) value indicating fineness of metal organization is raised near the combustion chamber of the cylinder head. (If an initial cooling speed of the molten metal is high, the DAS value is low, and vice versa).
As the DAS value is raised, quality of the entire cylinder head as well as mechanical properties such as strain and fatigue strength near the combustion chamber may be deteriorated.
In addition, such local cooling is used for preventing castings from contracting internally according to the conventional art, which causes the cooling cycle of the molten metal to be long. As a result, the cycle of casting processes may become long and productivity of the castings may be decreased according to the conventional art.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.